1. Field of the Invention
The present invention relates generally to electric power tools, and more particularly, to a direct-current electric power tool.
2. Description of the Related Art
The power source of a general electric power tool can be alternate current and direct current provided by a battery pack, wherein the latter is more popular than the former with common amateur users.
A commercially available direct-current power tool, such as U.S. Pat. Nos. 5,799,739 and 5,902,080, is primarily composed of a tool unit and a battery pack. The tool unit includes a coupling receptacle having a receiving chamber formed therein, an opening in communication with the receiving chamber, and an electrical contact disposed inside the chamber. The battery pack includes a connector protruded outwards and an electrical output contact. The connector of the battery pack is inserted into the chamber to enable the electrical output contact to electrically connect the electrical contact and to enable the battery pack to connect the tool unit.
The battery pack further includes a locking device having a button and a pawl. When the battery pack is connected with the coupling receptacle, the pawl engages with a block positioned on an inner periphery corresponding to the pawl to secure the battery pack to the tool unit from disengagement. When the user intends to remove the battery pack from the tool unit, it is easy to remove the battery pack from the tool unit by pressing the button to enable the pawl to disengage from the block.
The aforementioned connector and receiving chamber must have enough length and deepness to enlarge the contact area between the connector and the chamber to further enhance the cohesiveness between the battery pack and tool unit, thereby preventing the battery pack from shake which causes imperfect contact between the electrical output contact of the battery pack and the electrical contact of the tool unit. Hence, the battery pack and the tool unit will structurally and dimensionally enlarged to cause inconvenience for carrying the electric power tool.
Additionally, when the battery pack is connected with the tool unit, the pawl is directly burdened with the whole weight of the battery pack to easily damage the pawl or the block while the battery pack is slightly impacted to further cause the battery pack to disengage from the tool unit; this aforementioned drawback can be found in U.S. Pat. No. 5,799,739. Further, because the battery pack is controlled to disengage from the tool unit by one single button, it is easy to cause the user to carelessly touch the button to further cause the battery pack to disengage from the tool unit while operating the power tool.